3D Design Masterclass

Hey guys,

I figured this would be a great forum to start something like this, a "master class" so to speak based on the ins and outs, quirks and perks of doing your own 3d modelling.

I myself don't want to be the ONLY contributor, so if you have some special tips you've picked up on a certain program, share them!

A bit of a background:

I'm a final year dual degree student, majoring in Mechanical Engineering and Human Resources (apparently I'm one of the lucky few engineers with people skills), and my intent is to finish my Bachelors and go on into a Masters of Eng Project Management.

Although being reasonable at all areas of Engineering, my main/best areas of study are subjects related to industrial design and thermofluids. Hence I will be starting this thread with intent to teach people a few tricks.

OK, so here goes:

Programs:

When it comes to CAD/3D programs there is a literal boatload of them. They range from the basic web apps (TinkerCAD level), to the moderate ones (3DS Max), to the Engineering level programs (Solidworks, Inventor, Creo). My level of knowledge doesn't really concern programs like Tinker, even 3DS Max isn't something I use a lot of. My basic setup for modelling is Creo 2.0 (PTC), Solidworks (DSS), and Inventor (Autodesk), with the bulk of knowledge in Creo and Inventor.

At this stage, I won't go into details on the how to's of these programs because you can learn the way I did if you get stuck - Youtube has a host of videos on just about every aspect of these programs.

What I will do is try and give guidelines for modelling for printing for those of you who haven't done a lot of it, or give tips on why your model isn't working.

First Lesson: Fit and Tolerance.

This is my pet hate as an engineer, plain and simple. The one thing that irks me to no end, is someone sending me a file for printing, and me having to open the file, do a test print, work out something doesn't fit, rescale, and spend more resources printing it off again to fit. If I'm doing work for you as a commission, I'd rather see it come in non-STL format, something I can work with (3D CAD files!).

Now let's just say you wanted to print off something like a model engine. You submit all the files to someone like Shapeways or Materialise, get it back, and it doesn't go together. Pretty angry right? This is where fit and tolerance come into play.

If you have a round hole, diameter 10mm (~0.4in), and you have a peg you want to fit into it, what diameter would you make the peg? Answer: smaller than the hole!! But not too small. Fit determines whether this peg will fit inside the hole. Tolerance, however, determines how well you want it TO fit inside the hole. Do you want it to be loose or tight? Should it just rotate, or have room to move around? As a guide for 3D Printing, if I want a tight fit I work with ~0.1-0.15mm difference in size. Less tight, maybe able to rotate up to 0.3, and then loose up to 0.5. These are my guidelines, but there are many different tolerance options available. At the end of the day, as we've all worked out, printing isn't perfect. You will get some losses in translation between STL and G-Code, due to the limitations of current tech, so I always err on the side of "my printer is going to put too much material down".

Is there any other aspects of print modelling you have to give, or have a need to know about?

Robert (3D Accuracy),
In your blog on creating stl files you said:
"In the image above I’ve not only adjusted the chord height and angle control to be as fine as possible but I’ve also adjusted the step size to be as fine as possible. This creates the highest number of flat, triangulated surfaces that are as small as possible. At this quality level the curved surfaces on the part will be smooth and very nice in appearance.It’s also important to point out that the print time to create the part is not affected by the higher resolution stl file. The costs related to print time remain exactly the same while the quality of the 3D printed part goes way up."
How do you adjust chord height and angle control?

How come print time is not affected by the higher resolution?

Old Man Emu

@Old Man Emu,

I'm not sure about other programs but I know in Creo when exporting to STL format it lets me set those values. I haven't experienced that in SW or Inv yet though.

-Bliss

OME, if you are printing a three inch circle, it's about the same time and material if you make it out of 50 chords or 500 chords, but the 500 chord model will look much better. It will likely take longer to render in a viewer with more chords, but the printing times should be very similar.

-Davo

I'm using Rhino as my CAD program. I can't get the hang of all these new "touchy-feely" design programs.

I had a Eureka! moment this morning. Making more and more, smaller and smaller triangles is like calculating the area under a curve. All you are doing is dx, dy, dy as d approaches 0.

OME

i use rhino as well. i really enjoy that software. of course its not inventor or engineering cad software but its great for consumer products and more complex surfaces. maybe once i master it i will move onto solidworks

yes, you can tune it in to as fine as you want. its great at converting too. never had a model not solid or have errors.

jimc,
How do you tune the drawing when creating the stl?

OME

it asks you for the tolerance when exporting. i typically model in inches so my exports i usually have set to .001". i feel thats pretty adequate

Ahh, yes! I have seen that dialog box when exporting, and it is at a similar setting.

Old Man Emu